An unlikely candidate for 'world's meanest dog': The English cocker spaniel?

For the study, researchers at Spain's School of Veterinary Medicine at the Autonomous University of Barcelona crunched data related to more than 1,000 dog aggression cases logged at an area veterinary teaching hospital during the period of 1998-2006.

Of those cases, English cockers ranked the worst, followed by Rottweilers, boxers, Yorkshire terriers and German shepherd dogs. Discovery News has the details:

Probing the data further, [the study's lead author, Marta Amat] and her team discovered that English cocker spaniels were more likely than other dogs to act aggressively toward their owners as well as unfamiliar people. In contrast, dogs with reported behavior problems from other breeds tended to act aggressively toward other dogs. Among the English cocker spaniels, golden varieties and males were found to be the most hostile. ...

In terms of coat color, Amat explained that the coat pigment melanin shares a common biochemical pathway with dopamine and other brain chemicals involved in the control of aggressive behavior.

The results of the study mirror the findings of an earlier research team, also from Spain, conducted by scientists at the University of Cordoba. That study also found that male and golden-colored English cockers had a higher incidence of aggressive behavior than females or English cockers with other coat colors.

Authors of both studies are quick to note that ill-informed owners, or those who don't properly train their dogs, bear a great deal of the responsibility for their aggressive pets. From Discovery News:

Taking all possible reasons into consideration, [Joaquin Perez-Guisado of the University of Cordoba] and his team found that 40 percent of dominance aggression in dogs is associated with a lack of authority on the part of owners, who performed no, or minimal, obedience training.

According to Perez-Guisado and his team, "dogs that are trained properly do not normally retain aggressive dominance behavior."

English cocker spaniels (not to be confused with their American cocker spaniel cousins, which are, as their name suggests, more popular in the U.S.) are classified in the AKC's Sporting Group and historically helped hunters by flushing game birds. They typically weigh between 25 and 35 pounds and come in a wide variety of coat colors, including (according to the English Cocker Spaniel Club of America) golden, black, black/white, blue roan, liver, liver/white, liver roan, red, red/white, red roan, orange/white, orange roan, lemon/white, lemon roan, sable and sable/white.

The idea that cocker spaniels may have some predisposition to aggression is not a new one; animal behaviorist Dr. Roger Mugford wrote in the 1980s that English cockers were among the breeds most often referred to his clinic for behavior problems. (Mugford founded England's Animal Behaviour Centre and invented a common tool of the dog-training trade: the Halti headcollar).